Compact zoom lens

ABSTRACT

A zoom lens has a compact and simple structure, with satisfactorily corrected aberration and with a zooming ratio exceeding 2.0. The lens has a first lens group G 1  of a positive refractive power and a second lens group G 2  of a negative refractive power arranged in this order from the object side and effecting zooming operation by varying the distance of the lens groups. The first lens group G 1  has a front group G F  of a positive refractive power and a rear group G R  of a positive refractive power, arranged in this order from the object side. The front group G F  comprises a positive meniscus lens L 11  convex to the object side, a negative lens L 12  concave to the object side, a positive lens component L 13  and a positive lens component L 14 , arranged in this order from the object side. The rear group G R  comprises a positive lens L 15 , and the second lens group G 2  comprises a positive meniscus lens L 21  convex to the image side, a negative lens L 22  , and a negative meniscus lens L 23  concave to the object side, arranged in this order from the object side. The lens satisfies following conditions: 
     -0.8&lt;f 2  2/f W  &lt;-0.6 
     2.6&lt;f R  /f F  &lt;8 
     0.45&lt;f 14  /f W  &lt;1.26 
     -1.1&lt;f 22  /f W  &lt;-0.7 
     1.5&lt;Q 11  &lt;5 
     -0.5&lt;Q 12  &lt;1.3 
     -1.8&lt;Q 13  &lt;1 
     -3&lt;Q 21  &lt;-2 
     1.2&lt;Q 23  &lt;1.8 
     34&lt;ν 12  &lt;55.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens adapted for use in acompact camera such as a camera with lens shutter.

2. Related Background Art

Compact cameras with lens shutter have been more and more automated inrecent years, with various functions such as automatic focusing,automatic film loading, date recording, incorporated electronic flashetc. as standard equipment, and have become accepted by wider and widerusers. Recently there are also commercialized those with a lens ofmultiple focal lengths, for expanding the field of application further.

Zoom lens of simplest structure suitable for such compact cameras is atwo-group telescopic zoom lens composed of a first lens group G₁ of apositive refractive power and a second lens group G₂ of a negativerefractive power. In comparison with the usual lenses for single lensreflex cameras, such lens is more suitable for the cameras with lensshutter, having less restriction on the behind-lens focal length and canachieve compactization by reducing said behind-lens focal length to acertain extent.

However the zoom lenses of this kind proposed before are mostly withfocal length in a range of f =40-60 mm and F-number in a range of 4-5.6,and, even in bright lenses with high zooming ratios, the focal lengthand the F-number are still in ranges of f=35-70 mm and F=3.5-6.7.

Among such lenses, some are designed with an extremely short behind-lensfocal length in order to reduce the entire length of the lens.Consequently, even if compactization is achieved in this manner, theremay result internal reflections between the last lens face of the lenssystem and the film plane, eventually leading to the formation of ghostimage deteriorating the image quality. Besides the second lens group G₂positioned close to the film plane becomes inevitably large as thediameter thereof has to be close to the size of the film.

Also in such zoom lenses, since the refractive powers of the lens groupsare relatively limited in order to secure the imaging performance, thereis required a large moving amount for the lens groups for a given zoomratio, leading to a large lens system.

SUMMARY OF THE INVENTION

In consideration of the foregoing, the object of the present inventionis to provide a zoom lens which is free from the above-mentioneddrawbacks, and has a compact and simple structure, with satisfactorilycorrected aberration and with a zooming ratio exceeding 2.0.

The above-mentioned object can be attained, according to the presentinvention, by a compact zoom lens having a first lens group G₁ of apositive refractive power and a second lens group G₂ of a negativerefractive power arranged in this order from the object side andeffecting zooming operation by varying the distance of said lens groups;

wherein said first lens group G₁ has a front group G_(F) of a positiverefractive power and a rear group G_(R) of a positive refractive power,arranged in this order from the object side;

said front group G_(F) comprises a positive meniscus lens L₁₁ convex tothe object side, a negative lens L₁₂ concave to the object side, apositive lens component L₁₃ and a positive lens component L₁₄, arrangedin this order from the object side;

said rear group G_(R) comprises a positive lens L₁₅ ; and

said second lens group G₂ comprises a positive meniscus lens L₂₁ convexto the image side, a negative lens L₂₂, and a negative meniscus lens L₂₃concave to the object side, arranged in this order from the object side;and

wherein said zoom lens further satisfies following conditions:

    -0.8<f.sub.2 /f.sub.w <-0.6                                (1)

    2.6<f.sub.R /f.sub.F <8                                    (2)

    0.45<f.sub.14 /f.sub.W <1.26                               (3)

    -1.1<f.sub.22 /f.sub.W <-0.7                               (4)

    1.5<Q.sub.11 <5                                            (5)

    -0.5<Q.sub.12 <1.3                                         (6)

    -1.8<Q.sub.13 <1                                           (7)

    -3<Q.sub.21 <-2                                            (8)

    1.2<Q.sub.23 <1.8                                          (9)

    34<ν.sub.12 <55                                         (10)

in which:

f_(W) : focal length of entire zoom lens at the wide angle end;

f₂ : focal length of said second lens group G₂ ;

f_(F) : focal length of said front group G_(F) ;

f_(R) : focal length of said rear group G_(r) ;

f₁₄ : focal length of the positive lens component L₁₄ in said frontgroup;

f₂₂ : focal length of the negative lens L₂₂ in said second lens group;

Q₁₁ : shape factor of the positive meniscus lens L₁₁ in said frontgroup;

Q₁₂ : shape factor of the negative lens L₁₂ in said front group;

Q₁₃ : shape factor of the positive lens component L₁₃ in said frontgroup;

Q₂₁ : shape factor of the positive meniscus lens L₂₁ in said second lensgroup;

Q₂₃ : shape factor of the negative meniscus the L₂₃ in said second lensgroup; and

ν₁₂ : Abbe's number of the negative lens L₁₂ in said front group.

Thus the present invention can provide a zoom lens which, in a simpleand compact structure, has a zoom ratio exceeding 2.0 and satisfactorilycorrected aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3, 4, 5, 6, 7 and 8 respectively illustrate lens structuresin 1st to 8th embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now the present invention will be clarified in detail by preferredembodiments thereof shown in the attached drawings.

As shown in FIG. 1, the zoom lens of the present invention comprises afirst lens group G₁ of a positive refractive power and a second lensgroup G₂ of a negative refractive power, arranged in this order from theobject side, and effects zooming operation by varying the distance ofsaid lens groups;

wherein said first lens group G₁ comprises a front group G_(F) of apositive refractive power; and a rear group G_(R) of a positiverefractive power, arranged in this order from the object side;

said front group G_(F) comprises a positive meniscus lens L₂₁ having aconvex face to the object side; a negative lens L₁₂ having a concaveface to the object side; a positive lens component L₁₃ ; and a positivelens component L₁₄, arranged in this order from the object side;

said rear group G_(R) comprises a positive lens L₁₅ ; and

said second lens group G₂ comprises a positive meniscus lens L₂₁ havinga convex face to the image side; a negative lens L₂₂ ; and a negativemeniscus lens L₂₃ having a concave face to the object side, arranged inthis order from the object side.

Within the above-explained basic structure, the zoom lens of the presentinvention further satisfies following relations:

    -0.8<f.sub.2 /f.sub.W <-0.6                                (1)

    2.6<f.sub.R /f.sub.F <8                                    (2)

    0.45<f.sub.14 /f.sub.W <1.26                               (3)

    -1.1<f.sub.22 /f.sub.W <-0.7                               (4)

    1.5<Q.sub.11 <5                                            (5)

    -0.5<Q.sub.12 <1.3                                         (6)

    -1.8<Q.sub.13 <1                                           (7)

    -3<Q.sub.21 <-2                                            (8)

    1.2<Q.sub.23 <1.8                                          (9)

    34<ν.sub.12 <55                                         (10)

wherein:

f_(W) : focal length of entire zoom lens at the wide angle end;

f₂ : focal length of said second leng group G₂ ;

f_(F) : focal length of said front group G_(F) ;

f_(R) : focal length of said rear group G_(R) ;

f₁₄ : focal length of the positive lens component L₁₄ in said frontgroup;

f₂₂ : focal length of the negative lens L₂₂ in said second lens group;

Q₁₁ : shape factor of the positive meniscus lens L₁₁ in said frontgroup;

Q₁₂ : shape factor of the negative lens L₁₃ in said front group;

Q₁₃ : shape factor of the positive lens component L₁₃ in said frontgroup;

Q₂₁ : shape factor of the positive meniscus lens L₂₁ in said second lensgroup;

Q₂₃ : shape factor of the negative meniscus lens L₂₃ in said second lensgroup; and

ν₁₂ : Abbe's number of the negative lens L₁₂ in said front group.

The above-mentioned shape factor is defined by: ##EQU1## wherein r_(a),r_(b) are radii of curvature respectively of the object side and imageside of a lens component.

Also the positive lens component L₁₃ in said front group is preferablycomposed, in the order from the object side, of a negative lens L_(13n)and a positive lens L_(13p) adhered thereto, satisfying followingconditions:

    15<ν.sub.13p -ν.sub.13n                              (11)

    0.2<n.sub.13n -n.sub.13p                                   (12)

wherein:

ν_(13p) : Abbe's number of the positive lens L_(13p) in the positivelens component L₁₃ of said front group G_(F) ;

ν_(13n) : Abbe's number of the negative lens L_(13n) in the positivelens component L₁₃ of said front group G_(F) ;

n_(13n) : refractive index of the negative lens L_(13n) in the positivelens component L₁₃ of said front group G_(F) ; and

n_(13p) : refractive index of the positive lens L_(13p) in the positivelens component L₁₃ of said front group G_(F).

Also the positive lens component L₁₄ in said front group may becomposed, in the order from the object side, of a positive lens L_(14p)and a negative lens L_(14n) adhered thereto, satisfying the followingconditions:

    20<ν.sub.14p -ν.sub.14n                              (13)

    0.15<n.sub.14n -n.sub.14p                                  (14)

wherein:

ν_(14p) : Abbe's number of the positive lens L_(14p) in the positivelens component L₁₄ of said front group G_(F) ;

ν_(14n) : Abbe's number of the negative lens L_(14n) in the positivelens component L₁₄ of said front group G_(F) ;

n_(14p) refractive index of the negative lens L_(14n) in the positivelens component L₁₄ of said front group G_(F) ; and

n_(14p) refractive index of the positive lens L_(14p) in the positivelens component L₁₄ of said front group G_(F).

The above-explained structure of the present invention allows to reducethe entire length of the lens while securing a certain behind-lens focallength by providing each lens group with a stronger refractive force,and still enables to correct the aberrations which tend to aggravate dueto said stronger refractive force.

Firstly, the first lens group is given a stronger refractive force inorder to reduce the moving amounts of the first and second lens groupsG₁, G₂ thereby realizing a compact length while securing a certainbehind-lens focal length. Also the refractive force of the first lensgroup G₁ is shared by the front group G_(F) and the rear group G_(R)whereby the aberrations which generally result from a strongerrefractive force in a lens system can be extremely satisfactorilycorrected.

The variation in the curvature of the meridional image plane, resultingfrom zooming, can also be satisfactorily reduced, since positive andnegative image plane curvatures respectively generated by the frontgroup G_(F) and the rear group G_(R) can be balanced with a positiveimage plane curvature generated in the second lens group G₂.

Also the spherical aberration can be almost satisfactorily corrected bythe front group G_(F), so that the variation in the spherical aberrationcan be maintained extremely small in moving the front group G_(F) onlyat the focusing operation with the front lens group. In such structure,since the distance between the rear group G_(R) and the second lensgroup G₂ is constant, it is rendered possible to suppress the positionalchange, resulting from the focusing operation, of the diagonal rayentering the second lens group G₂. It is therefore possible to reduce,in well balanced manner, the variations in the image plane curvature andin the distortion aberration in a state focused to a short distance.

In the following there will be explained in detail the aforementionedconditions of the present invention.

The condition (1) is required in order to realize a compact total lengthwith a certain behind-lens focal length and a high zoom ratio, whileachieving satisfactory corrections of the various aberrations.

The condition (1) defines the optimum focal length of the second lensgroup G₂. Above the upper limit of the condition (1), the second lensgroup G₂ will have a stronger refractive power, which will beadvantageous for compactization and for a higher zoom ratio, butdisadvantageous for correcting aberrations. Particularly at the wideangle end, there will appear excessively large positive distortionaberration and image plane curvature, which are extremely difficult tocorrect. On the other hand, a range below the lower limit of thecondition (1) is undesirable, because compactization and high zoom ratioare extremely difficult to achieve though the corrections of aberrationsare easier. For achieving further compactization, the lower limit of thecondition (1) is preferably selected as -0.72.

The condition (2) defines the optimum ratio of refractive power of thefirst lens group shared by the front group G_(F) and the rear groupG_(R), for reducing the variation in the aberrations resulting from thefocusing operation, while reducing the aberrations generatedparticularly by the front group G_(F). In addition, in a structure withthe front group G_(F) and the rear group G_(R) arranged across adiaphragm respectively at the object side and at the image side, thiscondition (2) also serves to control the image plane curvatures of thefront and rear groups in well balanced manner, to balance said imageplane curvatures with the image plane curvature generated in the secondlens group G₂, and to satisfactorily reduce the variations in theaberrations in the focusing and zooming operations.

Above the upper limit of the condition (2), the refractive power of therear group G_(R) will become excessively weak, requiring a strongrefractive power in the front group G_(F) and resulting in a largenegative image plane curvature, whereby the variations of aberrations atzooming will become undesirably large. On the other hand, below thelower limit of the condition (2), the refractive power of the rear groupG_(R) will become excessively strong, thus resulting in an undesirablystrong spherical aberration.

The condition (3) defines the optimum focal length for the positive lenscomponent L₁₄ in the first lens group, for obtaining a high zoom ratio.A larger refractive power in said positive lens component L₁₄ will movethe principal point of the first lens group G₁ to the image side,whereby the air gap between the first and second lens groups can be madelarger when the distance of the principal points thereof is constant. Alarger air gap allows to extend the zoom ratio toward the telephotoside.

Above the upper limit of the condition (3), the refractive power of thepositive lens component L₁₄ will become weak, moving the principal pointof the first lens group G₁ toward the object side, whereby the air gapbetween the first and second lens groups cannot be made large. For thisreason a high zoom ratio is difficult to achieve.

On the other hand, below the lower limit the refractive power of thepositive lens component L₁₄ will become strong, moving the principalpoint of the first lens group G₁ to the image side. Thus a large air gapcan be realized between the first and second lens groups, facilitatingto obtain a high zoom ratio. However, the positive lens component L₁₄will generate an excessively large spherical aberration which isdifficult to correct.

The condition (4) defines the optimum focal length of the negative lensL₂₂ in the second lens group, in order to achieve satisfactorycorrection on the image plane curvature and on the positive distortionaberration at the wide angle end.

Above the upper limit of the condition (4), the negative lens L₂₂ willhave to have an excessively large negative refractive power in thesecond lens group G₂, whereby the variation in the image plane curvaturein the zooming operation will become excessively large, and asignificant positive distortion aberration will appear at the wide angleend. On the other hand, below the lower limit of the condition (4),though the refractive power shared by the negative lens L₂₂ in thesecond lens group G₂ is reduced, the negative lens component L₂₃,positioned behind said negative lens L₂₂, will be given a largerrefractive power. Thus, the variation of image plane curvature in thezooming operation will become excessively large, and a significantpositive distortion aberration will appear at the wide angle end, as inthe area above the upper limit of the condition (4).

The condition (5) defines the optimum shape of the positive lens L₁₁positioned closest to the object side in the first lens group, withrespect to the correction of the distortion aberration.

A zoom lens composed of positive and negative lens groups, as in thepresent invention, tends to generate a positive distortion aberrationparticularly at the wide angle end. In order to prevent such positivedistortion aberration, the positive lens L₁₁, positioned closest to theobject side in the first lens group of positive refractive power, isrequired to have a meniscus shape with a convex face directed to theobject side and satisfying the condition (5).

Above the upper limit of the condition (5), the spherical aberrationbecomes difficult to correct. On the other hand, below the lower limitof the condition (5), there will appear, at the wide angle end, asignificant positive distortion aberration which is extremely difficultto correct.

The condition (6) is related to the corrections of the sphericalaberration, distortion aberration and coma aberration, and defines theoptimum shape of the negative lens L₁₂ in the first lens group, forcorrecting these aberrations in well balanced manner.

The negative refractive power of the negative lens L₁₂ has to beincreased in order to correct the negative spherical aberrationgenerated in the first leng group G₁ of positive refractive power.However, a stronger curvature of the concave face, directed to theobject side, of the negative lens L₁₂ will generate an inwardly directedcoma aberration because a ray below the off-axis ray is subjected to astrong diverging effect at the wide angle end. On the other hand, aweaker curvature of said concave face, directed to the object side, ofthe negative lens L₁₂ will lead to an undesirably significant positivedistortion aberration at the wide angle end.

Also if the image-side face of said negative lens L₁₂ is composed of astrongly convex face directed to the image side, the object-side face ofsaid negative lens L₁₂ will have to be composed of a strongly concaveface directed to the object side. Such lens structure is howeverundesirable, because of the excessively inward coma aberration at thewide angle end.

Thus the condition (6) defines the lens shape optimizing the curvatureof the negative lens L₁₂ in the first lens group. Above the upper limitof the condition (6), the negative lens L₁₂ will assume a strongmeniscus shape with a concave face directed to the object side, whereinan excessive inward coma aberration will result from the strongcurvature of the face at the object side of said negative lens L₁₂. Onthe other hand, below the lower limit of the condition (6), the negativelens L₁₂ will have a weak curvature on the face at the object side,whereby the positive distortion aberration generated at the wide angleend will become extremely difficult to correct.

The condition (7) defines the optimum lens shape of the positive lenscomponent L₁₃ in the front group of the first lens group, forsatisfactorily correcting the spherical aberration generated in thefirst lens group G₁.

Outside the limits of the condition (7), the positive lens component L₁₃itself generates a significant spherical aberration which is difficultto correct.

The condition (8) defines the optimum shape of the positive lens L₂₁closest to the object side in the second lens group G₂, forsatisfactorily correcting the spherical aberration at the telephoto end.Because of its strong negative refractive power, the second lens groupG₂ tends to generate a positive spherical aberration particularly at thetelephoto end. For its well balanced correction, it is necessary togenerate a large negative spherical aberration at the positive lens L₂₁which is positioned closest to the object side in the second lens groupG₂. In this case said positive lens L₂₁ has to have a meniscus shapeconvex to the image side, in order to satisfy the condition (8).

Above the upper limit of the condition (8), the second lens group G₂generates a significant positive spherical aberration, thus destructingthe balance of aberrations in the entire lens system. On the other hand,below the lower limit of the condition (8), off-axis aberrationsaggravate at the wide angle end. More specifically, the higher ordercurvature of image plane increases to result in a significant comaaberration.

The condition (9) defines the optimum lens shape of the negative lensL₂₃ in the second lens group, in order to satisfactorily correct theoff-axis aberrations at the wide angle end. For satisfactorilycorrecting the positive distortion aberration, negative image planecurvature etc. which tend to significantly appear at the wide angle end,the negative lens L₂₃ has to have a meniscus shape concave to the objectside, so as to satisfy the condition (9).

Outside the limits of the condition (9), the off-axis aberrations,particularly the distortion aberration and the image plane curvature,become difficult to correct at the wide angle end.

The condition (10) defines the optimum Abbe's number for the negativelens L₁₂ of the first lens group G₁, in order to satisfactorily correctthe color aberration, particularly the magnification color aberration.

The object-side face of said negative lens L₁₂ has a function ofsignificantly diverging the incident ray, and has a shape particularlyadversary to the off-axis ray.

Below the lower limit of the condition (10), the object-side face ofsaid negative lens L₁₂ will tend to generate a higher-order curvature ofthe magnification color aberration, which is difficult to correct. Onthe other hand, above the upper limit of the condition (10), the axialcolor aberration will become difficult to correct, because of the smalldifference in Abbe's number between said negative lens and the positivelens L₁₁ or the positive lens component L₁₃ in the first lens group.

For further satisfactory correction of the spherical aberration and thecolor aberration, it is desirable to form the positive lens componentL₁₃ or the position lens component L₁₄ in the first lens group G₁ byadhered positive and negative lenses.

In case the positive lens component L₁₃ in the first lens group iscomposed of adhered lenses, it is preferable to form said adheredlenses, in the order from the object side, by a negative lens L_(13n)and a positive lens L_(13p) adhered thereto, and it is more preferableto satisfy following conditions:

    15<ν.sub.13p -ν.sub.13n                              (11)

    0.2<n.sub.13n -n.sub.13p                                   (12)

wherein:

ν_(13p) : Abbe's number of the positive lens L_(13p) in the positivelens component L₁₃ of said front group G_(F) ;

ν_(13n) : Abbe's number of the negative lens L_(13n) in the positivelens component L₁₃ of said front group G_(F) ;

n_(13n) : refractive index of the negative lens L_(13n) in the positivelens component L₁₃ of said front group G_(F) ; and

n_(13p) : refractive index of the positive lens L_(13p) in the positivelens component L₁₃ of said front group G_(F).

The condition (11) defines the optimum difference in Abbe's number forachieving a higher dispersion in the negative lens L_(13n) than in thepositive lens L_(13p) of the positive lens component L₁₃.

Outside the limits of the condition (11), the magnification coloraberration and the axial color aberration will become extremelydifficult to correct.

The condition (12) defines the optimum difference in refractive indexfor achieving a higher refractive index in the negative lens L_(13n)than in the positive lens L_(13p) in the positive lens component L₁₃.

Outside the limits of said condition (12), satisfactory correction ofthe spherical aberration will become difficult.

Also in case the positive lens component L₁₄ in the first lens group G₁is composed of adhered lenses, they are preferably composed, in theorder from the object side, of a positive lens L_(14p) and a negativelens L_(14n) adhered thereto, and more preferably satisfy followingconditions:

    20<ν.sub.14p -ν.sub.14n                              (13)

    0.15<n.sub.14n -n.sub.14p                                  (14)

wherein:

ν_(14p) : Abbe's number of the positive lens L_(14p) in the positivelens component L₁₄ of said front group G_(F) ;

ν_(14n) : Abbe's number of the negative lens L_(14n) in the positivelens component L₁₄ of said front group G_(F) ;

n_(14n) : refractive index of the negative lens L_(14n) in the positivelens component L₁₄ of said front group G_(F) ; and

n_(14p) : refractive index of the positive lens L_(14p) in the positivelens component L₁₄ of said front group G_(F).

The condition (13) defines the optimum difference in Abbe's number forrealizing a higher dispersion in the negative lens L_(14n) than in thepositive lens L_(14p) adhered thereto, in the positive lens componentL₁₄.

Outside the limits of said condition (13), the axial color aberrationwill become difficult correct.

The condition (14) defines the optimum difference in refractive index,for realizing a higher refractive index in the negative lens L_(14n)than in the positive lens L_(14p) in the positive lens component L₁₄.

Outside the limits of the condition (14), the spherical aberrationcannot be fully corrected, so that satisfactory correction of thespherical aberration will become difficult.

When the first lens group G₁ is solely composed of the front group G_(F)and the rear group G_(R) as in the present invention, the focusingoperation is preferably achieved by the movement of the front groupG_(F) only. Such focusing operation allows to minimize the variations inthe aberrations.

[Examples]

The present invention will be further clarified by examples thereof,concerning on compact zoom lenses of focal lengths of 36-78 mm andF-numbers of 3.6-7.8.

FIGS. 1 to 8 are respectively views showing lens structures of 1st to8th examples of the present invention.

Each of the examples has a basic structure same as that of the 1stembodiment shown in FIG. 1, consisting, in the order from the objectside of a first lens group G₁ which in turns consists of a front groupG_(F) composed of a positive meniscus lens L₁₁ convex to the objectside, a negative lens L₁₂ and positive lenses L₁₃, L₁₄, and a rear groupG_(R) composed of a positive lens L₁₅, and of a second lens group G₂composed of a positive meniscus lens L₂₁ convex to the image side, anegative lens L₂₂, and a negative meniscus lens L₂₃ concave to theobject side, with a diaphragm stop S positioned between the front groupG_(F) and the rear group G_(R).

In the 2nd example, the positive lens L₁₂ in the front group consists ofadhered lenses composed, in the order from the object side, of anegative lens L_(13n) and a positive lens L_(13p) adhered thereto.

In the 3rd to 8th examples, the positive lens L₁₄ in the front groupconsists of adhered lenses composed, in the order from the object side,of a positive lens L_(14p) and a negative lens L_(14n) adhered thereto.

In each of the examples, the focusing operation is conducted by axialmovement of the front group G_(F) only, while the zooming operation isconducted by axial movement of the first lens group G₁ and the secondlens group G₂ together toward the object side, in such a manner that theair gap therebetween is reduced.

Parameters of the 1st to 8th examples of the present invention arerespectively shown in Tabs. 1 to 8, wherein the numbers in the left-handcolumn indicate the order from the object side; r is the radius ofcurvature of the lens face; d is the distance between lens faces or thethickness of a lens; and Abbe's number and refractive index n are givenby the values for d-line (λ=587, 6 nm).

                  TABLE 1                                                         ______________________________________                                        (Example 1)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 61.4° ˜ 31.2°               F-number:         3.6˜ 7.7                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       15.276    2.55       54.6  1.51454                                    2       41.199    2.40                                                        3       -18.216   1.50       43.3  1.84042                                    4       20.273    1.00                                                        5       26.298    5.90       60.3  1.51835                                    6       -14.175   0.15                                                        7       25.498    3.20       82.6  1.49782                                    8       -76.411   (d 8)                                                       9       125.408   1.20       70.1  1.51860                                    10      -125.408  (d10)                                                       11      -37.346   2.70       28.6  1.79504                                    12      -16.086   1.70                                                        13      -15.768   1.20       33.9  1.80384                                    14      -37.517   2.30                                                        15      -14.368   1.30       45.4  1.79668                                    16      -63.175   (B f)                                                       ______________________________________                                        f       36.0437       55.0940 78.0057                                         d 8      2.6326        2.6326  2.6326                                         d10     10.818         4.8699  1.5639                                         B f      9.3794       27.6282 49.5760                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        (Example 2)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 61.2° ˜ 31.1°               F-number:         3.6˜ 7.7                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       16.334    2.55       54.6  1.51454                                    2       30.012    2.40                                                        3       -15.872   1.50       47.5  1.78797                                    4       ∞   1.00                                                        5       ∞   1.30       47.5  1.78797                                    6       20.195    3.90       70.2  1.48749                                    7       -13.386   0.15                                                        8       20.190    3.20       70.2  1.48749                                    9       -56.685   (d 9)                                                       10      124.972   1.20       64.1  1.51680                                    11      -124.972  (d11)                                                       12      -37.346   2.70       28.6  1.79504                                    13      -16.086   1.70                                                        14      -15.768   1.20       33.9  1.80384                                    15      -37.517   2.30                                                        16      -14.368   1.30       45.4  1.79668                                    17      -63.175   (B f)                                                       ______________________________________                                        f       36.0437       55.0940 78.0057                                         d 9      2.6195        2.6195  2.6195                                         d11     10.8185        4.8695  1.5635                                         B f      9.3794       27.6282 49.5760                                         ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        (Example 3)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 61.4° ˜ 31.1°               F-number:         3.6˜ 7.7                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       17.433    2.90       49.1  1.53172                                    2       64.652    1.80                                                        3       -28.785   2.00       40.9  1.79631                                    4       18.781    2.00                                                        5       32.171    4.50       38.1  1.60342                                    6       -54.513   0.60                                                        7       39.143    4.60       56.0  1.56883                                    8       -10.223   1.70       28.6  1.79504                                    9       -16.962   (d 9)                                                       10      145.857   1.20       60.7  1.60311                                    11      -145.856  (d11)                                                       12      -37.346   2.70       28.6  1.79504                                    13      -16.086   1.70                                                        14      -15.768   1.20       33.9  1.80384                                    15      -37.517   2.30                                                        16      -14.368   1.30       45.4  1.79668                                    17      -63.175   (B f)                                                       ______________________________________                                        f       36.0441       55.0948 78.0071                                         d 9      2.6064        2.6064  2.6064                                         d11     10.8398        4.8908  1.5848                                         B f      9.3796       27.6287 49.5770                                         ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        (Example 4)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 60.9° ˜ 31.1°               F-number:         3.6˜ 7.7                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       17.966    2.90       45.9  1.54814                                    2       38.705    1.80                                                        3       -25.215   2.00       40.9  1.79631                                    4       18.736    0.30                                                        5       25.395    6.00       40.8  1.58144                                    6       -40.028   0.60                                                        7       30.293    4.60       56.0  1.56883                                    8       -10.922   1.70       28.8  1.79504                                    9       -17.826   (d 9)                                                       10      145.930   1.20       38.1  1.60342                                    11      -145.933  (d11)                                                       12      -37.348   2.70       28.6  1.79504                                    13      -16.086   1.70                                                        14      -15.768   1.20       33.9  1.80384                                    15      -37.517   2.30                                                        16      -14.368   1.30       45.4  1.79668                                    17      -63.175   (B f)                                                       ______________________________________                                        f       36.0440       55.0945 78.0066                                         d 9      2.6928        2.6928  2.6928                                         d11     10.8399        4.8909  1.5849                                         B f      9.3795       27.6285 49.5766                                         ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        (Example 5)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 61.5° ˜ 31.2°               F-number:         3.6˜ 7.8                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       15.855    3.30       45.9  1.54814                                    2       55.214    1.80                                                        3       -32.377   2.00       45.4  1.79668                                    4       14.430    2.00                                                        5       23.497    4.00       60.3  1.51835                                    6       -49.678   0.60                                                        7       37.615    4.60       49.0  1.53172                                    8       -9.497    1.70       25.5  1.80458                                    9       -14.401   (d 9)                                                       10      125.330   1.30       60.3  1.51835                                    11      -125.330  (d11)                                                       12      -35.552   2.80       25.5  1.80458                                    13      -15.907   1.80                                                        14      -14.971   1.00       25.5  1.80458                                    15      -38.073   2.60                                                        16      -14.368   1.20       55.6  1.69680                                    17      -76.229   (B f)                                                       ______________________________________                                        f       36.0456       55.0977 78.0124                                         d 9      2.5319        2.5319  2.5319                                         d11     10.5805        4.6315  1.3255                                         B f      9.2949       27.5452 49.4954                                         ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        (Example 6)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 61.1° ˜ 31.1°               F-number:         3.6˜ 7.8                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       16.064    3.30       45.9  1.54814                                    2       34.852    2.20                                                        3       -27.264   1.70       45.4  1.79668                                    4       14.350    0.70                                                        5       19.364    5.50       59.0  1.51823                                    6       -36.513   0.20                                                        7       28.962    4.60       49.0  1.53172                                    8       -10.025   1.70       25.5  1.80458                                    9       -14.931   (d 9)                                                       10      131.141   1.30       56.4  1.50137                                    11      -131.141  (d11)                                                       12      -35.421   2.80       25.5  1.80458                                    13      -15.791   1.80                                                        14      -14.773   1.00       25.5  1.80458                                    15      -38.073   2.60                                                        16      -14.368   1.20       55.6  1.69680                                    17      -73.062   (B f)                                                       ______________________________________                                        f       35.9970       55.0071 78.0200                                         d 9      2.6026        2.6026  2.6026                                         d11     10.6069        4.6532  1.3279                                         B f      9.2221       27.4321 49.4763                                         ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        (Example 7)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 60.7° ˜ 31.1°               F-number:         3.6˜ 7.8                                              ______________________________________                                        r             d          Abbe    n                                            ______________________________________                                        1       15.720    3.30       49.0  1.53172                                    2       31.974    2.05                                                        3       -25.324   1.70       45.4  1.79668                                    4       13.392    0.37                                                        5       16.525    5.50       59.0  1.51823                                    6       -31.803   0.20                                                        7       27.072    4.60       49.0  1.53172                                    8       -10.870   1.70       25.5  1.80458                                    9       -15.406   (d 9)                                                       10      135.651   1.30       69.9  1.51860                                    11      -135.651  (d11)                                                       12      -34.578   2.80       25.5  1.80458                                    13      -15.527   1.80                                                        14      -14.559   1.00       25.5  1.80458                                    15      -39.036   2.60                                                        16      -13.855   1.20       55.6  1.69680                                    17      -66.874   (B f)                                                       ______________________________________                                        f       35.9978       55.0092 78.0238                                         d 9      2.5868        2.5868  2.5868                                         d11     10.1505        4.5747  1.4605                                         B f      9.3901       27.1616 48.6752                                         ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        (Example 8)                                                                   ______________________________________                                        Focal length:     f = 36.0˜ 78.0                                        Image angle:      2 ω = 60.7° ˜ 31.1°               F-number:         3.6˜ 7.8                                              ______________________________________                                               r      d          Abbe    n                                            ______________________________________                                        1       16.116    3.30       45.9  1.54814                                    2       32.991    2.08                                                        3       -24.979   1.70       45.4  1.79668                                    4       13.126    .40                                                         5       16.161    5.50       64.1  1.51680                                    6       -30.605   .20                                                         7       27.335    4.60       49.0  1.53172                                    8       -10.895   1.70       25.5  1.80458                                    9       - 15.302  (d 9)                                                       10      218.227   1.20       64.1  1.51680                                    11      -108.027  (d11)                                                       12      -37.337   2.80       25.8  1.78472                                    13      -15.804   1.80                                                        14      -14.848   1.00       25.5  1.80458                                    15      -40.004   2.60                                                        16      -13.934   1.20       55.6  1.69680                                    17      -72.667   (B f)                                                       ______________________________________                                        f       35.9995       54.9996 78.0010                                         d 9      2.5180        2.5180  2.5180                                         d11     10.0856        4.5091  1.3934                                         B f      9.6062       27.4444 49.0390                                         ______________________________________                                    

Tab. 9 shows the parameters of the 1st to 8th examples of the presentinvention, corresponding to the above-explained conditions of thepresent invention.

                  TABLE 9                                                         ______________________________________                                        (Parameters corresponding to the conditions                                   ______________________________________                                         Ex.                                                                                    ##STR1##                                                                              ##STR2##                                                                                  ##STR3##                                                                            ##STR4##                                  ______________________________________                                        1        -0.676  3.798       1.077 -0.963                                     2        -0.676  3.798       0.859 -0.963                                     3        -0.676  3.798       0.720 -0.963                                     4        -0.676  3.798       0.671 -0.963                                     5        -0.677  3.798       0.680 -0.869                                     6        -0.677  4.187       0.632 -0.850                                     7        -0.647  4.295       0.612 -0.816                                     8        -0.649  4.665       0.609 -0.830                                     ______________________________________                                        Ex.    Q.sub.11 Q.sub.12                                                                              Q.sub.13  Q.sub.21                                                                            Q.sub.23                              ______________________________________                                        1      2.179     0.053  -0.300    -2.513                                                                              1.589                                 2      3.388     1.000  -1.00     -2.513                                                                              1.589                                 3      1.738    -0.210  0.258     -2.513                                                                              1.589                                 4      2.733    -0.147  0.224     -2.513                                                                              1.589                                 5      1.806    -0.383  0.358     -2.619                                                                              1.465                                 6      2.710    -0.310  0.307     -2.609                                                                              1.490                                 7      2.934    -0.308  0.316     -2.630                                                                              1.523                                 8      2.910    -0.311  0.309     -2.468                                                                              1.474                                 ______________________________________                                                        ν.sub.13p --                                                                       n.sub.13n -                                                                           ν.sub.14p -                                                                      n.sub.14n -                             Ex.    ν.sub.12                                                                            ν.sub.13n                                                                          n.sub.13p                                                                             ν.sub.14n                                                                        n.sub.14p                               ______________________________________                                        1      43.3                                                                   2      47.5     22.7    0.3005                                                3      40.9                     27.4  0.2262                                  4      40.9                     27.4  0.2262                                  5      45.4                     23.5  0.2729                                  6      45.4                     23.5  0.2729                                  7      45.4                     23.5  0.2729                                  8      45.4                     23.5  0.2729                                  ______________________________________                                    

I claim:
 1. A compact zoom lens having, in the order from the objectside, a first lens group G₁ of a positive refractive power and a secondlens group G₂ of a negative refractive power and effecting zoomingoperation by varying the distance of said lens groups;wherein said firstlens group G₁ comprises, in the order from the object side, a frontgroup G_(F) of a positive refractive power and a rear group G_(R) of apositive refractive power; said front group G_(F) having, in the orderfrom the object side, a positive meniscus lens L₁₁ with a convex facedirected to the object side, a negative lens with a concave facedirected to the object side, a positive lens component L₁₃ and apositive lens component L₁₄ ; said rear group G_(R) having a positivelens L₁₅ ; wherein said second lens group G₂ comprises, in the orderfrom the object side, a positive meniscus lens L₂₁ with a convex facedirected to the image side, a negative lens L₂₂, and a negative meniscuslens L₂₃ with a concave face directed to the object side; and said zoomlens further satisfying following conditions: -0. 8<f₂ /f_(W) <-0.6(1)ti 2.6<f_(R) /f_(F) <8 (2)

    0.45<f.sub.14 /f.sub.W <1.26                               (3)

    -1.1<f.sub.22 /f.sub.w <-0.7                               (4)

    1.5<Q.sub.11 <5                                            (5)

    -0.5<Q.sub.12 <1.3                                         (6)

    -1.8<Q.sub.13 <1                                           (7)

    -3<Q.sub.21 <-2                                            (8)

    1.2<Q.sub.23 <1.8                                          (9)

    34<ν.sub.12 <55                                         (10)

wherein: f_(w) : focal length of entire zoom lens at the wide angle endthereof; f₂ : focal length of said second lens group G₂ ; f_(F) : focallength of said front group G_(F) ; f_(R) : focal length of said reargroup G_(R) ; f₁₄ : focal length of positive lens component L₁₄ in saidfront group; f₂₂ : focal length of negative lens L₂₂ in said second lensgroup; Q₁₁ : shape factor of positive meniscus lens L₁₁ in said frontgroup; Q₁₂ : shape factor of negative lens L₁₂ in said front group; Q₁₃: shape factor of positive lens component L₁₃ in said front group; Q₂₁ :shape factor of positive meniscus lens L₂₁ in said second lens group;Q₂₃ : shape factor of negative meniscus lens L₂₃ in said second lensgroup; and ν₁ : Abbe's number of negative lens L₁₂ in said front group.2. A compact zoom lens according to claim 1, wherein the positive lenscomponent L₁₃ in said front group is composed, in the order from theobject side, of a negative lens L_(13n) and a positive lens L_(13p)adhered thereto, and further satisfying following conditions:

    15<ν.sub.13p -ν.sub.13n                              ( 11)

    0.2<n.sub.13n -n.sub.13p                                   ( 12)

wherein: ν_(13p) : Abbe's number of positive lens L_(13p) in thepositive lens component L₁₃ of said front group G_(F) ; ν_(13n) : Abbe'snumber of negative lens L_(13n) in the positive lens component L₁₃ ofsaid front group G_(F) ; n_(13n) : refractive index of negative lensL_(13n) in the positive lens component L₁₃ of said front group G_(F) ;and n_(13p) : refractive index of positive lens L_(13p) in the positivelens component L₁₃ of said front group G_(F).
 3. A compact zoom lensaccording to claim 1, wherein the positive lens component L₁₄ in saidfront group is composed, in the order from the object side of a positivelens L_(14p) and a negative lens L14n adhered thereto, and furthersatisfying following conditions:

    20<ν.sub.14p -ν.sub.14n                              ( 13)

    0.15<n.sub.14n -n.sub.14p                                  ( 14)

wherein: ν_(14p) : Abbe's number of positive lens L_(14p) in thepositive lens component L₁₄ of said front group G_(F) ; ν_(14n) : Abbe'snumber of negative lens L_(14n) in the positive lens component L₁₄ ofsaid front group G_(F) ; ν_(14n) refractive index of negative lensL_(14n) in the positive lens component L₁₄ of said front group G_(F) ;and ν_(14p) : refractive index of positive lens L_(14p) in the positivelens component L₁₄ of said front group G_(F).
 4. A compact zoom lensaccording to claim 1, wherein the focusing operation is conducted byaxial movement of the front group G_(F) alone of said first lens groupG₁.